Subject: [Simple] IMDN issue #8: List-Action, Original-From and Original-Message-ID

From: Hisham Khartabil <[email-masked]>
Date: Fri, 27 Jan 2006 16:18:30 +0100

I don't think the List-Action header is needed. The Original-From 
header and Original-Message-ID may not be needed also. this depends on 
how we define the behaviour of the IM exploder to be.

To summarise:

- List-Action header is used to indicate if a B2BUA  or UAS is to do 
the reporting
- Original-From allows a UAS to know there to send the notification if 
there was a B2BUA like an exploder on the path.
- Original-Message-ID allows a UAS to indicate to the UAC the 
message-ID of the original message that the notification is for. This 
is also when a B2BUA is involved.

All 3 headers are above to help the case that a UAC chooses for the UAS 
to send the notifications directly instead of the B2BUA generating them 
indicating the B2BUA's receipt of the message.

I would design it as follows:

- UAC indicates, in the IM, its wish to receive an IMDN
- B2BUA forwards the IM with the necessary original-from and 
original-message-id headers (if needed)
- the UAS generates the IMDN and sends it just like it would send an IM 
to the UAC. For MSRP, it would be just like a SEND request in the other 
direction. For SIP MESSAGE, it would use the from (or original-from) 
and to headers in the incoming IM to create the MESSAGE request in the 
reverse direction. Same applies for message-id.
- If it was not possible for the B2BUA to reach the UAS, it would 
generate its own IMDNs for that IM.

Regards,
Hisham

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